Polymorphs can differ in such physical and chemical (i.e. physiochemical) properties as crystal shape, density, hardness, color, chemical stability, melting point, hygroscopicity, suspendability and dissolution rate, and such biological properties as biological availability. Predicting physiochemical properties for a crystal form or crystal forms in which the solid state of a chemical compound can exist remains impossible.
Also, the single enantiomers of pharmacologically active compounds have met an increased interest in the last years because of improved pharmacokinetic and biological properties. Therefore, there is a need for a process that can be used in large scale for the preparation of the single enantiomers of afoxolaner. Generally, asymmetric processes for obtaining chiral molecules afford optically active molecules in enantiomerically enriched forms rather than in pure single enantiomeric forms unless the processes include resolution methods. Therefore, there is also a need for a method that can be used in large scale for the enhancement of enantiomeric purity of optically active (S)-afoxolaner.
Afoxolaner may exist as two enantiomeric configurations, namely the (S)-enantiomer which is the compound of formula (Ia):

and the (R)-enantiomer, which is a compound of formula (Ib):

Furthermore, even predicting whether the solid state of a compound may be present in more than one crystal form is not possible.
U.S. patent application Ser. No. 62/319,207, which is the priority document for U.S. patent application Ser. No. 15/480,316 published as US 2017/0311601 A1 (all incorporated herein by reference) discloses a compound of formula (Ia) and methods for its preparation, as well as the utility of this compound as an invertebrate pest control agent. New solid forms of this compound have now been discovered.
U.S. Pat. No. 8,410,153, incorporated herein by reference, describes afoxolaner as being effective in treating or preventing parasitic infections or infestations in or on animals.